The full name of HDL is high-density lipoprotein cholesterol (HDL-C), and its ideal range of HDL-C is >1.04mmol/L (>40mg/dL), and it is low if it is <0.91mmol/L (<35mg/dL). Currently, HDL is considered to be one of the important protective factors in the body to prevent cardiovascular and cerebrovascular diseases caused by atherosclerosis. The causes of low HDL may include: 1. genetic factors causing lower HDL: genetic factors are one of the main factors of HDL level; some people only show low HDL, not accompanied by elevated triglycerides, LDL, etc., as simple low HDL; another part of people with low HDL and at the same time, triglycerides and/or LDL This is called hyperlipidemia and often requires medication. Common diseases include familial hypercholesterolemia, familial hypertriglyceridemia, familial mixed hyperlipidemia, etc.; 2. Decreased HDL caused by related diseases: such as acute myocardial infarction, liver disease, kidney disease, surgery, burns, etc. will also show decreased HDL; 3. Other factors. Such as high-fat diet, smoking, lack of exercise situation, some people will also show reduced HDL. There may be genetic, disease and lifestyle-related reasons for lower HDL. Reduced HDL with hyperlipidemia requires medication; current research has found that HDL can be raised through a healthy diet, moderate exercise, and weight loss to prevent atherosclerotic disease.